XPost: sci.physics   
      
   In article <79cf0a8.0310111116.cc6d740@posting.google.com>, sbha   
   ris@ix.netcom.com (Steve Harris  sbharris@ROMAN9.netcom.com) writes:   
   >mmeron@cars3.uchicago.edu wrote in message news:...   
   >   
   >> Yes.  Complicated stuff.  What you end up with is a "sandwich   
   >> shielding", a set of layers, each with a specific function.  We do it   
   >> already.  When you want to shield against fast neutrons, you need a   
   >> sandwich of moderator-neutron_absorber_gamma absorber.  You can think   
   >> up more complex configurations.   
   >   
   >Yes. And you need a sandwich for spallation neutrons which are 20% of   
   >the radiation in some cases, and which come off of 30 or 40 heavy ion   
   >species at a very wide range of energies.   
   >   
   >> >No simple answers to any of this. On doing a little research I find   
   >> >that much of the needed data and analysis hasn't even been collected   
   >> >or done.   
   >> >   
   >> Its not that bad.  Most if not all of the information required exists,   
   >> you just need to put it together into a design.   
   >   
   >COMMENT   
   >   
   >Nope you underestimate this. Truely.  There are monte carlo quantum   
   >codes for heavy ion radiation transport in solid matter.   
      
   There is much more than just this.  Heavy ions, protons,   
   ultra-relativistic electrons, gammas, neutrons and all possible mixes.   
   How much you'll find in the open literature, that's another story.   
      
    But that's   
   >just the beginning. You have to know the input flux of heavy ions not   
   >only in interplanetary space, but also on the Martian surface, where   
   >the atmosphere has greatly screwed things up and changed the character   
   >of the radiation (more neutrons!) but not blocked very many rads. We   
   >know this muchy, but we know too little of the character of radiation   
   >on the Martian surface to model effects on humans that well, yet.   
   >It's a major question on future Mars robotic missions.   
   >   
   >Then you have the problem that heavy ion biological effects are the   
   >most poorly studied of all known radiation effects, and here they're a   
   >major player.   
      
   Only if you shield very poorly.  The reason heavy ion biological   
   effects are the most poorly studied, is because heavy ions are the   
   easiest to block.  It is only when their kinetic energy, per nucleon,   
   exceeds their binding energy (again, per nucleon), that spallation   
   effects become a bitch.  But you don't encounter many heavy ions in   
   this range.   
   >   
   >For every phase you have that 3-element neutron sheild design, but you   
   >have to do it THREE times, and in three separate ways.   
   >   
   Not really.  A neutron shield is a neutron shield.  One which is   
   designed for the highest energy neutrons you expect to face is good   
   for all the rest, as well.  The problem with neutron shields is that   
   there is really no way to make them compact.  You need sufficient   
   thickness for moderation.   
      
   So, basically, you've to plan on sufficient thickness to stop the fast   
   protons, followed by a sufficient thickness, from this point, to   
   moderate the neutrons.  And the you've to absorb the thermal neutrons   
   and provide sufficient thickness, from this point, to absorb most of   
   the resulting gammas.  That's quite bulky.   
      
   Mati Meron                      | "When you argue with a fool,   
   meron@cars.uchicago.edu         |  chances are he is doing just the same"   
      
   --- SoupGate-Win32 v1.05   
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